Low amperage fuse



May 18, 1954 E. v. SUNDT LOW AMPERAGE FUSE Filed May 18, 1953 INVENOR. jag/47 d fljwrzdf 9 M Y Patented May 18, 1954 UNITED STATES PATENT OFFICE LOW AMPERAGE FUSE Edward V. Sundt, Wilmette, Ill.

Application May 18, 1953, Serial No. 355,541

12 Claims. 1

This invention relates to electric fuses for protecting electric circuits from overload conditions.

The principal object of this invention is to provide an improved fuse which is particularly useful in protecting low energy or amperage circuits, such as may be encountered in circuits using transistors or the like, which embodies a new principle of construction and operation, which produces new and improved results, and which may be inexpensively manufactured.

Generally, the improved principle of construction and operation of the electric fuse of this invention is very much like that disclosed in my copending application Serial No. 355,542 filed May 18, 1953 wherein the end of an elongated or rod or pin shaped conductor engages a thin sheet conductor at a point within th area of the thin sheet conductor. Preferably, the transverse dimensions of the point of engagement of the conductors is greater than the thickness of the thin conductor. These conductors are connected in series with the electric circuit to be protected so that, upon a predetermined overload in the electric circuit fusion takes place in the thin conductor about the point of engagement of the conductors and provides an ever widening gap between the conductors. In the operation of such an electric fuse, the fuse blows on high overloads because the high current density, in the area of the thin conductor around the point of engagement of the conductors, heats up the thin conductor to its fusion temperature for instantly melting the same. The fuse blows on a sustained low overload because the point of engagement of the conductors heats up to the fusion temperature of the thin conductor by reason of current passage therethrough for melting the thin con ductor. Because the fusion of the thin conductor provides an ever widening gap, a gap is provided over which the circuit voltage cannot maintain conduction and the are, if any, after. striking, is unable to establish itself in one place long enough to cause damage. The establishment of sustained arc is therefore prevented and the arc is quickly extinguished.

In accordance with the invention herein the electric fuse is so constructed that it will protect low energy or amperage circuits, such as may be encountered in circuits using transistors and the like. Here there is provided a platform of electrical insulating material which carries and supports a thin film conductor of fuse metal and theend of an elongated conductor engages this thin film conductor at a point within the area thereof. The thin film conductor is preferably less than substantially .001 inch in thickness and is preferably applied to the supporting platform by evaporating the fuse metal and condensing the same thereon. The point of engagement between the conductors is made quite small, substantially .001 inch in transverse dimension, and towards this end the end of the elongated conductor is preferably pointed. Preferably, the film is also deposited on the elongated conductor at the point of engagement to insure good contact between the two conductors. When these conductors are connected in series in an electric circuit and an overload condition occurs, fusion takes place in the area of the thin film conductor about the point of engagement to provide an ever widening gap between the conductors as pointed out above.

A very efficient fuse is provided in this manner by reason of the fact that the amount of fuse metal that must be melted is very small as compared to a wire or a punched element fuse. The small amount of energy required to melt the thin film of fuse metal is an outstanding advantage of this construction. With all this, the fuse is rugged because the thin film of fuse metal is firmly supported by the platform. The fuse metal used in the thin film conductor is selected on the basis of the amperage at which the fuse is to blow. For example, for a real low ampere fuse, high resistance metals may be used, such as bismuth, antimony, lead, tin or the like, and for higher ratings, a lower resistance material, such as, silver or aluminum are more desirable.

The electric fuse of this invention may take various forms, but preferably it includes a substantially cylindrical body of electrical insulating material having a bore extending longitudinally from one end and a notch in the side thereof communicating with the inner end of the bore for forming the platform on which is deposited the thin film conductor of fuse metal. The elongated conductor extends through and is supported in the bore in the body and its inner end is preferably pointed and engages the thin film conductor on the platform. Metallic caps may be applied to the ends of the body and electrically connected to the conductors for facilitating the connecting of the fuse into the electric circuit to be protected.

Further objects of this invention reside in the details of construction of the low amperage fuse and in the cooperative relationships between the component parts thereof.

Other objects and advantages of this invention will become apparent to those skilled in the art upon reference to the accompanying specification, claims and drawing in which:

Figure l is a side elevational view of the low amperage fuse of this invention.

Figure 2 is an end view thereof.

Figure 3 is a vertical sectional view through the fuse taken substantially along the line E 3 of Figure 1.

Figure l is a view similar to Figure 1, but with the metallic caps omitted.

Figure is a sectional view taken substantially along the line 5-5 of Figure 3.

The low amperage fuse of this invention is generally designated at Id. It includes a substantially cylindrical body II formed of insulating material, such as may be moulded from a thermoplastic material such as nylon or the like. This body II is provided with a longitudinally extending bore i2 which runs from one end of the body to a point within the body. A notch I3 is provided in the side of the body and it communicates with the inner end of the bore I2. The notch I3 and the inner end of the bore #2 form a substantially flat platform M within the body.

A thin film of fuse metal is suitably applied to the platform I4 to form a thin film conductor I 5. Preferably this film is formed by evaporating the fuse metal and then condensing the onto the platform Ill in order to obtain the thin film. The thickness of the film is preferably less than .001 inch and may be as thin as ten millionths of an inch. The fuse metal may be any desired metal. For a very low ampere fuse high resistance metals are preferably used, such as bismuth, antimony, lead, tin and the like, bismuth being preferred. For higher ratings a lower resistance metal may be used, such as silver or aluminum. This thin film conductor I5 of fuse metal so applied to the platform M is firmly supported thereby.

The end of the body II adjacent the notch I3 is preferably coated with tin or copper by spraying the same, this coating being designated at I6. When this coating is applied it is brought into contact with the film I5 of the fuse metal so as to be electrically connected thereto. In this connection the thin film I5 of fuse metal may be deposited over the side of the body as well as on the platform as illustrated in Figure 3 so that the sprayed metal iii physically engages the same and has a large contact therewith. Conversely a portion of the sprayed metal i6 may be carried onto the film I5 of fuse metal at the outer edge of the platform I l. Likewise the other end of the body II may also be sprayed with tin or copper or the like as indicated at H.

An elongated conductor I8 formed of copper, steel or any other suitable conducting metal, which may take the form of a pin is inserted into the bore l2. The inner end of this elongated conductor is preferably pointed and en-- gages the thin film conductor I5 at the point of engagement designated at I9. The transverse dimension, that is the diameter of the point of engagement I9, is preferably about .001 inch. To assure good electrical contact between the elongated conductor I8 and the thin film conductor I5, the film is preferably vaporized on the point thereof. The elongated conductor I8 is firmly held within the bore 12 of the body II. Suitable metallic caps 20 and 2i are applied over the ends of the body II and are held in place thereon by the sprayed metal I6 and IT. The cap 2%! is in electrical contact with the sprayed metal I6 and hence the thin film conductor I5 of the fuse metal and the cap 2| engages and is in elec trical contact with the elongated conductor I3. These metal caps facilitate the connection of the fuse into the electric circuit to be protected thereby.

When the fuse is connected in the electrical circuit and an overload condition occurs, fusion takes place in the area of the thin film conductor I5 about the point of engagement [9 to provide an ever widening gap between the conductors. The fuse blows promptly upon the occurrence of high overload conditions because of the high current density in the area of the thin film conductor I5 immediately around the point of engagement I9 of the conductors. This immediately heats up the thin film conductor I5 to its fusion temperature for instantly melting the same. The fuse also blows on a sustained low overload condition because the current flow through the point of engagement I9 heats the point of engagement up to the fusion temperature of the thin film conductor I5, and when this temperature is reached the thin film conductor I5 fuses about the point of engagement I 9. Because the fusion of the thin film conductor provides an ever widening gap, a gap is provided over which the circuit voltage cannot maintain conduction and the are, if any, after striking is unable to establish itself in one place long enough to cause damage. The fuse of this invention constructed in this manner is very efficient because of the fact that the amount of fuse metal that must be melted is very small. This small amount of energy required to melt the thin film conductor of fuse metal is an outstanding advantage of the construction of the fuse of this invention. The electric fuse of this invention is rugged in nature for the thin film conductor which would normally be quite fragile is firmly supported by the platform and is fully enclosed within the fuse.

The fuse of this invention may be made extremely small and the only real requirement on size is to make the same so that it may be con-- veniently manufactured on a production basis and readily handled. For example, the fuse may be about /2 inch in length and A; inch in diameter. Thus, the fuse of this invention be ing small is mechanically fitted as well as electrically fitted for use in protecting low energy circuits, such as circuits incorporating transistors or the like.

While for purposes of illustration one form of this invention has been disclosed other forms thereof may become apparent to those skilled in the art upon reference to this disclosure and, therefore, this invention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. A low amperage fuse comprising a platform of electrical insulating material, a thin film conductor of fuse metal carried by the platform, an elongated conductor having its end engaging the thin film conductor at a point within the area thereof, and means for connecting the conductor in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin in conductor about the point to provide an ever widening gap between the conductors.

2. A low amperage fuse comprising a platform of electrical insulating material, a thin film conductor of fuse metal applied to the platform by evaporating the fuse metal and condensing the same thereon, an elongated conductor having its end engaging the thin film conductor at a point within the area thereof, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

3. A low amperage fuse comprising a platform of electrical insulating material, a thin film conductor of fuse metal carried by the platform, an elongated conductor having a pointed end engaging the thin film conductor at a point within the area thereof, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

4. A low amperage fuse comprising a platform of electrical insulating material, a thin film conductor of fuse metal applied to the platform by evaporating the fuse metal and condensing the same thereon, an elongated conductor having a pointed end engaging the thin film conductor at a point within the area thereof, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

5. A low amperage fuse comprising a platform of electrical insulating material, a thin film conductor of fuse metal carried by the platform, an elongated conductor having its end engaging the thin film conductor at a point within the area thereof, the transverse dimension of the point of engagement of the conductors being greater than the thickness of the thin film conductor, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

6. A low amperage fuse comprising a platform of electrical insulating material, a thin film conductor of fuse metal carried by the platform and. having a thickness of less than substantially 01 inch, an elongated conductor having its end engaging the thin film conductor at a point within the area thereof, the transverse dimension of the point of engagement of the conductors being substantially .001 inch, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

7. A low amperage fuse comprising a platform of electrical insulating material, a thin film conductor of fuse metal carried by the platform, an elongated conductor having its end engaging the thin film conductor at a point within the area thereof, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined high overload in the electric circuit or a predetermined low overload existing for a time interval, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

Iii

8. A low amperage fuse comprising a hollow tube having an end wall forming a platform in the tube and formed of insulating material, a thin film conductor of fuse metal carried by the platform in the tube, an elongated conductor carried in the tube and having its end engaging the thin film conductor at a point within the area thereof, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

9. A low amperage fuse comprising a substantially cylindrical body of insulating material having a bore extending longitudinally from one end thereof and a notch in the side thereof communicating with the inner end of the bore and forming a platform in the body, a thin film conductor of fuse metal. carried by the platform in the body, an elongated conductor carried in the bore in the body and having its end engaging the thin film conductor at a point within the area thereof, and means for connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

10. A low amperage fuse comprising a hollow tube having an end wall forming a platform in the tube and formed of insulating material, a thin film conductor of fuse metal carried by the platform in the tube, an elongated conductor carried in the tube and having its end engaging the thin film conductor at a point within the area thereof, a metallic cap carried by each end of the tube, means for electrically connecting the thin film conductor to one of the caps, means for electrically connecting the elongated conductor to the other cap, and said caps connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

11. A low amperage fuse comprising a substantially cylindrical body of insulating material having a bore extending longitudinally from one end thereof and a notch in the side thereof communicating with the inner end of the bore and forming a platform in the body, a thin film conductor of fuse metal carried by the platform in the body, an elongated conductor carried in the bore in the body and having its end engaging the thin film conductor at a point within the area thereof, a metallic cap carried by each end of the body, means for electrically connecting the thin film conductor through the notch to one of the caps, means for electrically connecting the elongated conductor to the other cap, and said caps connecting the conductors in series in an electric circuit so that, upon a predetermined overload in the electric circuit, fusion takes place in the area of the thin film conductor about the point to provide an ever widening gap between the conductors.

12. A low amperage fuse comprising a platform of electrical insulating material, an elongated conductor arranged substantially normal to the platform and having a pointed end substantially contacting the platform at a point within the area thereof, a continuous thin film conductor References Cited in the file of this patent Number UNITED STATES PATENTS Name Date Sheller Mar. 31, 1931 Baldwin et 'al. Feb. 3., 1942 Loporto Apr. 25, 1950 

